JPS6312326A - Exhaust gas treating apparatus for painting dryer furnace - Google Patents

Abstract

PURPOSE:To carry out stable operation for a long period by passing the exhaust gas through a dust removing filter, a heat exchanger, and then a rotary catalyst device mounting a primary catalyst, circulating a part of gas through the painting dryer furnace, and discharging the other part to the outside of the system after the oxidation treatment by a secondary catalyst. CONSTITUTION:The exhaust gas which flows out from the painting dryer furnace 21 is passed through a 1st low passage 22 into the dust removing filter 25 where the dust is removed, heated through a heat exchanger 26, and entered a rotary catalyst device 28 where the gas is passed through a flow passage A, inflammable elements in the gas are oxidized by the primary catalyst 30 and streamed again into the primary catalyst 30 through a reversing space 33 to be heated, and then the gas is cooled in the heat exchanger 26. Next, the exhaust gas is streamed into a 2nd flow passage 37, and a part of the gas is entered the painting dryer furnace 21 to be circulated, and the other part is passed through a 3rd flow passage 39 branched from the flow passage 37, passed through the secondary catalyst 41 where a small amount of inflammable elements are oxidized, and discharged to the outside of the system.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a paint drying furnace in which exhaust gas containing volatilized solvent components emitted within the paint drying furnace is oxidized to be odorless and discharged outside the system. facing the exhaust gas treatment equipment.

"Prior art and its problems" For example, in paint drying ovens used in the steel industry, painted strips are baked through a drying process that evaporates the solvent in the paint and causes the components of the paint film to react. The coating is heated to achieve the required paint film performance. However, as the production volume of steel increases, the concentration of solvent gas in the paint drying oven increases, and if the exhaust gas containing this is discharged directly outside the system, it may cause environmental pollution, so it is necessary to reduce the concentration of solvent gas in the exhaust gas. need to be lower.

For this purpose, the exhaust gas containing solvent is taken out from the paint drying oven, passed through a catalyst layer, and flammable components derived from solvents such as ketones, cellosolves, toluene, and xylene are burned to reduce their J degree. By using a circulation system that returns most of the clean gas to the furnace, the concentration of solvent gas in the exhaust gas outside the system is kept below a predetermined value.

FIG. 2 shows an example of a conventional paint drying furnace for exhaust gas treatment. That is, a steel material is introduced into the paint drying oven 1 as shown by the white arrow in the figure, and the solvent in the paint is volatilized and removed under an atmosphere of, for example, about 180°C. Solvent 1, for example, mainly consists of ethyl cellosolve, and the concentration in the exhaust gas is, for example, 2500 pp of ethyl cellosolve.
It is said to be m.

Then, the exhaust gas in the paint drying oven 1 is drawn by the fan 2 and taken out to the first flow path 3. At this time, the amount of the exhaust gas taken out is adjusted by the damper 4.

The exhaust gas taken out into the first flow path 3 is guided to a cross-flow type heat exchanger 5 and heated there. Further, if necessary, fuel such as butane-air mixed gas is inputted from the auxiliary combustion snowmaking 6 and combusted to raise the exhaust gas temperature to a catalyst activation temperature of about 350°C. In this state, the exhaust gas is transferred to the catalyst 7.
to oxidize the combustible components in the exhaust gas.

The solvent components in the combustion exhaust gas are oxidized and burned by this catalyst 7, and tar mist and flammable dust in the exhaust gas are also oxidized and burned.
Once adsorbed on the catalyst surface, it reacts and is removed by tP. Incidentally, the non-flammable dust is removed from the exhaust gas by adhering to the catalyst 7 or being filtered out. The code 8 is the catalyst 7
It is a blind lid with one end i = z.

The combustion exhaust gas that has passed through the catalyst 7 and has been heated by combustion of combustible components and from which non-flammable dust has been removed passes through the heat exchanger 5 and is cooled by exchanging heat with the exhaust gas before oxidation treatment. ,
A part of it (for example, 415 fluids) is returned to the coating drying furnace 1 through the 20th flow path 9, and the remaining part (for example, 1
15 flow rate) branched from the second flow path 10.
is discharged from the system through the

The exhaust gas returned through the second flow path 9 is guided to the paint drying oven 1 by a recycling fan 11. Further, a burner 12 is provided next to the recycle fan 11 to raise the temperature of the gas circulating in the furnace. In addition, the code 13.
Reference numeral 14 denotes a damper that adjusts the flow rates of the exhaust gas returned to the coating drying oven 1 and the exhaust gas discharged to the outside of the system.

However, when designing the exhaust gas treatment for this paint drying oven, if the exhaust gas contains catalyst poisoning components such as 5Ox (sulfur oxides), not only the catalyst surface layer but the entire catalyst will be poisoned. As the process progresses, the catalyst deteriorates and the purification efficiency decreases. For this reason, flammable components in the exhaust gas cannot be sufficiently removed, causing the environmental pollution mentioned above.Also, when the flammable components generated from the paint drying oven are malodorous components, the Because the concentration of malodorous components in the paint is not sufficiently reduced, malodors are generated in the exhaust gas released into the atmosphere and in the paint drying oven.

In general, pollutable dust, tar mist, etc. are difficult to purify even if they are adsorbed on the catalyst surface, so they clog the catalyst and increase pressure loss, resulting in poor system pressure matching. Circulating gas! may need to be reduced, or operations may become unstable.

Therefore, in order to perform stable operation, it is necessary to constantly monitor the deterioration status of the catalyst and replace it if the catalyst has deteriorated. However, when replacing the catalyst, it is necessary to stop the operation, and the replacement cost becomes very high because the catalytic element itself carries a metal and the like.

In addition, in this exhaust gas treatment device for a paint drying oven, dust and tar tend to adhere to the heat transfer element of the heat exchanger, and this adhesion causes a decrease in the heat transfer performance of the heat exchanger and an increase in pressure loss. Therefore, the temperature of the gas flowing into the catalyst decreases, and the purification efficiency of the catalyst deteriorates. In general, the outlet temperature of the catalyst decreases, and the amount of heat exchanged by the heat exchanger further decreases.

Therefore, it becomes necessary to compensate for the decrease in the temperature of the gas flowing into the catalyst by reheating using the auxiliary tjA sintering device, which increases fuel costs.

On the other hand, when attempting to remove combustible components present in the exhaust gas at a high concentration of, for example, 2,500 ppm, by oxidizing it with a catalyst to a concentration of, for example, 100% or less, using the above-mentioned exhaust gas treatment device. , the entire amount of exhaust gas is passed through the catalyst 7 to be treated, and most of the exhaust gas (for example, 115) whose combustible component concentration has been significantly reduced by the catalyst treatment passes through the 20th flow path 9 again and becomes combustible. It will be returned to the paint drying oven 1, which is the source of the components. Therefore, it is necessary to increase the volume of the expensive catalyst 70, and there is also a waste of recontaminating most of the exhaust gas that has been sufficiently purified.

“Objective of the Invention” The object of the present invention is to stabilize the performance of the catalyst for a long time by preventing poisoning of the catalyst by SOX etc. in the exhaust gas, and to prevent dust and tar from entering the heat transfer element of the heat exchanger. To provide an exhaust gas treatment device for a paint drying oven that prevents pressure loss and heat exchange performance deterioration due to adhesion and can stably remove flammable components (malodorous components) contained in exhaust gas over a long period of time.

"Structure of the Invention" The exhaust gas treatment device for a paint drying furnace according to the present invention includes a first flow path for taking out a predetermined amount of exhaust gas from the paint drying furnace;
a dust removal filter provided in the flow path, a flow path on the heat receiving fluid side that raises the temperature of the exhaust gas introduced from the first flow path, and a heat radiation fluid side that lowers the temperature of the exhaust gas after the combustible components have been oxidized. a heat exchanger equipped with a flow path, a rotary catalyst device equipped with a primary catalyst that oxidizes combustible components of exhaust gas introduced from a flow path on the heat receiving fluid side of the heat exchanger, and a rotary catalyst device equipped with a second flow path for circulating a part of the exhaust gas that has been oxidized and passed through the flow path on the heat radiation fluid side of the heat exchanger to the paint drying furnace; and a second flow path that branches from the second flow path and the remainder of the exhaust gas. a third flow path for discharging the water out of the system;
The present invention is characterized in that a secondary catalyst is provided in the middle of the flow path to further oxidize combustible components contained in the remainder of the exhaust gas.

In this way, in the present invention, the exhaust gas taken out in the first flow path is passed through a heat exchanger and a rotary catalytic device connected thereto, from which dust has been removed in advance by a dust removal filter placed in the middle of the flow path. be introduced. Therefore, it is possible to prevent dust from adhering to the heat transfer element of the heat exchanger or the primary catalyst of the rotary catalyst device.

In addition, for the oxidation treatment of combustible components, a rotary catalyst device is used in which heating gas and heated gas flow alternately periodically, and this is connected to the flow path on the heat receiving fluid side and the flow path on the heat dissipating fluid side of the heat exchanger. Therefore, even if the primary catalyst of the rotary catalytic converter is poisoned, it will self-regenerate when it comes into contact with the high-temperature heating gas, and even if tar mist or the like adheres to the primary catalyst, that part will then be removed from the heating gas side. When this happens, it comes into contact with high-temperature heated gas and is purified, making it difficult for tar etc. to accumulate on the secondary catalyst. Therefore, it is possible to maintain the catalyst groove ff stably for a long period of time, to suppress gas pressure loss as much as possible, to maintain good heat transfer performance, and to perform stable operation for a long period of time.

Further, by providing the secondary catalyst in the middle of the third flow path, it is possible to further oxidize the low J degree combustible components contained in the remainder of the exhaust gas.

In this way, by treating the exhaust gas discharged outside the system again with the secondary catalyst, combustible components remaining due to leaks in the rotary catalytic converter can be more completely removed. In this case, the exhaust gas flowing into the flow path of the cake 3 is the remainder of the exhaust gas returned to the coating drying oven, so its flow rate is small, and therefore the required volume of the catalyst is also small.

According to a preferred aspect of the present invention, a temperature-raising auxiliary device for introducing fuel gas or high-temperature gas is provided between the flow path on the heat-receiving fluid side of the heat exchanger and the rotary catalyst bag or inside the rotary catalyst device. It is being

According to this, during start-up operation, etc., the temperature of the exhaust gas decreases due to heat storage in the heat transfer element of the heat exchanger, but the temperature of the exhaust gas is raised by the fuel gas or high temperature gas, so the next catalyst The outlet temperature becomes high and the start-up operation time can be shortened. Also,
- When the primary catalyst is severely poisoned, the poisoned primary catalyst can be activated by increasing the temperature of the exhaust gas.

"Embodiment of the Invention" FIG. 1 shows an embodiment of the present invention for treating snowmaking in an exhaust gas treatment oven for a paint drying furnace.

A first flow path 22 for extracting exhaust gas is connected to the paint drying oven 21. This first flow path 22 has a damper 23 that adjusts the flow tv of exhaust gas and a fan 24 that is located downstream of this damper 23 and sucks the exhaust gas in the middle of the flow path. Therefore, the flow of the exhaust gas from the paint drying oven 21 is adjusted to a predetermined amount by the damper 23, and is taken out to the first flow path 22 by the fan 24.

On the downstream side of the fan 24 in the middle of the first flow path 22,
A dust removal filter 25 is arranged. This dust removal filter 25 removes dust from the exhaust gas taken out from the first flow path 22, and its filter body is made of a ceramic porous body, a cloth made of ceramic fiber, glass fiber, etc. It is preferable to use this in order to prevent corrosion caused by SOx.

The dust filter 25 is equipped with a backwashing mechanism (not shown).
The increase in pressure loss is suppressed by backwashing the filter body at regular intervals.

In the first flow path 22 further downstream of the dust removal filter 25,
The heat exchanger 26 (with which the heat exchanger 26 is disposed) has a built-in heat transfer element (not shown), and this heat transfer element is provided with a flow path on the heat receiving fluid side and a flow path on the heat radiation fluid side. It is being The flow path on the heat receiving fluid side has a function of raising the temperature of the exhaust gas from the first flow path 22, and is connected to the heated gas flow path of the rotary catalyst device 28 via the injection flow path 27. . Also, is the flow path on the heat dissipation fluid side a rotary catalyst bag? l12
It has a function of lowering the temperature of the exhaust gas from the rotary catalyst bag N28, and is connected to the heated gas flow path B of the rotary catalyst bag N28 via a return flow path 29.

The rotary catalytic device 28 includes a primary catalyst 30 that oxidizes combustible components in exhaust gas, and a narrow portion thereof is fixed to a drive shaft 31 and rotated by a morph 32 .

In the rotation path of the secondary catalyst 30, half is used as a heated gas flow path A, and the other half is used as a heated gas flow path B. Therefore, the exhaust gas introduced from the flow path on the heat receiving fluid side of the heat exchanger 26 via the injection flow path 27 is transferred to the flow path A.
When passing through, the combustible components are oxidized by the secondary catalyst 30 and the temperature becomes high. Then, the exhaust gas is transferred to the inversion space 33
Then, it turns around and passes through the flow path 8&, where it passes through the primary catalyst 30 again and becomes very hot. The exhaust gas whose combustible components have been oxidized by the secondary catalyst 30 is returned to the flow path on the heat radiation fluid side of the heat exchanger 26 via the return flow path 29.

The secondary catalyst 30 is preferably one in which platinum, palladium, or a mixture of both is supported on a ceramic honeycomb-shaped carrier.In this secondary catalyst 30, the poisoned portion of the secondary catalyst 30 through which low-temperature gas flows is exposed to high-temperature gas. It has the property of being able to self-regenerate upon contact.

In addition, for the second day of the rotary catalytic converter, the -th catalyst 30 is fixed,
In contrast, the channels A and B may be configured to rotate relative to each other.

A temperature raising auxiliary device 34 is connected to the pouring path 27 that connects the heat exchanger 26 and the rotary catalyst device f2. This heating aid device! 34 indicates that the exhaust gas temperature has risen to the catalyst activation temperature during start-up operation, or that the primary catalyst 3 has been significantly poisoned.
The fan 35 is used for activating the 0 catalyst, etc., and includes a fan 35 for sending fuel gas and high-temperature gas to the injection channel 27, and a valve 36 for controlling the introduction of the gas. Instead of or in addition to being connected to the pouring path 27, such a temperature raising auxiliary device 34 is connected to the rotary catalyst device 28 as shown by the two-dot chain line in the figure, and is connected to the rotary catalyst device 12B.
Fuel gas or high temperature gas may be introduced into the inversion space 33.

Roughly speaking, a second flow path 37 is connected to the flow path on the heat radiation fluid side of the heat exchanger 26 . This second flow path 37 circulates most of the oxidized exhaust gas to the coating drying furnace 21, and a damper 38 is provided in the middle thereof to adjust the flow rate of the exhaust gas.

A 30th flow path 39 is branched from the second flow path 37 . This third flow path 39 is for discharging the remaining part of the exhaust gas to the outside of the system, and a damper 40 is provided in the middle thereof to adjust the flow rate of the exhaust gas.

A secondary catalyst 41 is provided in the middle of the third flow path 39 and downstream of the damper 40 . This secondary catalyst 41 is for roughly and completely oxidizing a small amount of combustible components still remaining in the exhaust gas to be discharged outside the system. The secondary catalyst 41 is preferably one in which platinum, palladium, or a mixture of both is supported on a ceramic honeycomb carrier.

An air preheater 42 is provided downstream of such a third flow path 39.
is connected. This flue preheater 42 is for exchanging heat with the burner preheated air for the exhaust gas from which combustible components have been completely removed by the secondary catalyst 41, and discharging the exhaust gas to the outside air through the chimney 43.

Further, a flow path 44 is connected to the air preheater 42, and burner preheated air is guided to each burner 45 through this flow path 44. Then, the gas inside the paint drying oven 21 is passed through the fan 46.
During the circulation, it is heated by a burner 45.

Next, the operation of the exhaust gas treatment ordnance for the paint drying oven according to the present invention will be explained.

From inside the paint drying oven 21, for example, 4.2% carbon dioxide,
Water 11.0%, Nitrogen 74.0%, Oxygen 10.4%, Ethyl Cellosolve 2500ppm, SOx 300ppm
m, dust Ar1a.

I m+/Nrn', tar concentration 2.5 mq/Nm,
Exhaust gas with a temperature of 230℃ flows ji 2000ONmi'
/h to be taken out to the first flow path 22.

The exhaust gas is sent to the fan 2 while the flow rate is adjusted by the damper 23.
4 into the first flow path 22, and the dust is removed by the dust removal filter 25. Therefore, it is possible to prevent dust from adhering to the heat transfer element built into the heat exchanger 26 and the primary catalyst 30 of the rotary catalyst device 28. The exhaust gas then flows into the flow path on the heat-receiving fluid side of the heat exchanger 26, and is heated by the heat transfer element to 300° C. at which the primary catalyst 30 has the required activity.

In the rotary catalyst device 28, the secondary catalyst 30 is rotated at a predetermined period by a motor 32, and the exhaust gas heated by the heat exchanger 26 is sent to the flow path A in No. 2B of the same table via the outflow path 27. Inflow. In this flow path A, the exhaust gas flows through -1! ! 30, the odoriferous combustible component (ethyl cellosolve) is oxidized and deodorized. - The catalyst volume of the second catalyst 30 is such that the purification efficiency is 90% or more. -Next catalyst 3018
The temperature of the passing exhaust gas is raised to 443° C. due to the heat of oxidation. The exhaust gas whose flow is then reversed in the reversal space 33 shown in No. 28 of the same table enters the flow path B, and after passing through the second catalyst 30 again, the remaining odorous combustible components in the exhaust gas are roughly oxidized and deodorized. The sample was then treated with a temperature of 488° C. At this time, the ethyl cellosolve concentration was 250 ppm.

This high-temperature exhaust gas is sent to the heat exchanger 26 again via the return flow path 29, passes through the flow path on the heat radiation fluid side of the heat exchanger 26, and is lowered in temperature to 418°C. As a result, heat exchanger 2
The heat transfer element in 6 becomes high temperature and obtains heat to raise the temperature of the exhaust gas introduced from the first flow path 22.

By the way, in the flow path A of the rotary catalyst device 28, the temperature of the exhaust gas that contacts the secondary catalyst 30 is as low as 300°C, so the secondary catalyst 30 is temporarily poisoned by SOx. The portion that has received I moves toward the flow path 8 side by rotation by the motor 32 and comes into contact with exhaust gas at a high temperature of 418° C., so that it self-regenerates and recovers its purification performance. Also,
Tar mist adhering to the primary catalyst 30 in the low-temperature flow path A also comes into contact with high-temperature exhaust gas as it rotates to become the flow path B, and is purified by vaporization or combustion.

During start-up operation, the exhaust gas temperature decreases due to heat storage in the heat transfer element in the heat exchanger 26, but in this case, the temperature increase auxiliary device 34 is activated to pump the fuel gas and high-temperature gas back and forth. It is introduced into the rotary catalyst device f28 via the flow path 27. By introducing fuel gas, the concentration of odorous flammable components in the exhaust gas is increased, and the heat of oxidation at the secondary catalyst 30 is increased, thereby raising the temperature of the primary catalyst 30. Even when high-temperature gas is introduced, the temperature of the primary catalyst 30 is increased. The temperature can be raised, reducing startup time. -The next catalyst 30 is poisoned,
Even if self-regeneration is hindered, the poisoned primary catalyst 30 can be activated by operating the temperature raising auxiliary device 34 and introducing fuel gas or high temperature gas.

At the outlet of the rotary catalytic converter 28, the concentration of ethyl cellosolve in the exhaust gas increases to 365p due to leakage from the seal.
pm, but this exhaust gas passes through the heat exchanger 26, the second flow path 37, the flow rate is adjusted by the damper 38, and the I 700ONm' /M) It is circulated. In addition, the remaining part of the exhaust gas, that is, 30
00 Nrr? /h passes through a third flow path 39 branched from the 20th flow path 37, whose flow rate is adjusted by a damper 40, and is roughly oxidized by a secondary catalyst 41.The secondary catalyst 41 has a purification efficiency of 99%. The catalyst volume is said to be above,
Ethyl cellosolve, which was contained in the exhaust gas before treatment at 365 ppm, is reduced to 4 ppm.

Therefore, in combination with the secondary catalyst 30 and the secondary catalyst 41, a total of 99.8% or more of ethyl cellosolve is purified. In this case, the amount of exhaust gas passing through the secondary catalyst 41 is 300
0 Nm/h, the catalyst volume required to obtain a purification efficiency of 99% or more is relatively small, and combustible components can be effectively removed with a small total catalyst volume.

The exhaust gas purified in this way passes through the air 2 preheater 42 and exchanges heat with the burner preheated air at room temperature, and then passes through the chimney 43.
and is released into the atmosphere. The heated burner preheated air is guided to the burner 45 through the flow path 44 and then to the paint drying furnace 2.
1 will be reintroduced.

"Effects of the Invention" As explained above, according to the present invention, the exhaust gas taken out from the paint drying oven is passed through a dust removal filter in advance, and then introduced into the heat transfer element of the heat exchanger and the subsequent rotary catalyst device. This makes it possible to prevent dust from adhering to the heat transfer element and the catalyst. In addition, for the oxidation and deodorization treatment of exhaust gas, a rotary catalyst device is used in which heated gas and heated gas alternately flow, and this is connected to the flow path on the heat-receiving fluid side and the flow path on the heated fluid side of the heat exchanger. Therefore, even if the primary catalyst of a rotary catalytic converter is poisoned by, for example, SOx,
It can self-regenerate when it comes into contact with high-temperature exhaust gas, and even if tar mist or the like adheres to the heat transfer element or primary catalyst of the heat exchanger, it can be purified by the high-temperature exhaust gas. Therefore, the activity of the catalyst can be kept stable for a long time,
By suppressing gas pressure loss as much as possible and maintaining good heat transfer performance, exhaust gas can be purified stably over a long period of time. In addition, by providing a secondary catalyst in the third flow path, even if the secondary catalyst does not remove the odoriferous combustible components or if there is a leak mainly in the rotary catalytic converter, the secondary catalyst The catalyst can remove odoriferous and combustible components to a desired level and discharge them out of the system.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the exhaust gas treatment bag for a paint drying oven according to the present invention, and FIG. 2 is a schematic diagram showing an example of a conventional exhaust gas treatment device for a paint drying oven. In the figure, 211. a coating drying oven, 22 is the first flow path, 25
is a dust removal filter, 26 is a heat exchanger, 28 is a rotary catalyst device, 30 is a primary catalyst, 34 is a temperature raising auxiliary device, 37 is a second flow path, 39 is a third flow path, 41 is a secondary catalyst, 42 is an air preheater. Patent applicant: Asahi Glass Co., Ltd. Agent: Sumitomo Metal Industries, Ltd. Patent attorney: Matsui Counter-question: Patent attorney: Kunio Miura Patent attorney: Yoshimi Sasayama Figure 2

Claims (2)

[Claims] (1) A first flow path that takes out a predetermined amount of exhaust gas from the paint drying oven, a dust removal filter provided in this first flow path, and a heat receiver that raises the temperature of the exhaust gas introduced from the first flow path. a heat exchanger including a flow path on the fluid side and a flow path on the heat dissipating fluid side that lowers the temperature of the exhaust gas after oxidizing the combustible components;
A rotary catalyst device including a primary catalyst that oxidizes combustible components of exhaust gas introduced from a flow path on the heat receiving fluid side of the heat exchanger; a second flow path that circulates a part of the exhaust gas that has passed through the flow path to the paint drying furnace; and a third flow path that branches from the second flow path and discharges the remainder of the exhaust gas to the outside of the system. An exhaust gas treatment device for a paint drying furnace, comprising: a secondary catalyst that further oxidizes combustible components contained in the remainder of the exhaust gas in the middle of the third flow path. (2) In claim 1, a temperature-raising auxiliary device that introduces fuel gas or high-temperature gas between the flow path on the heat-receiving fluid side of the heat exchanger and the rotary catalyst device or into the rotary catalyst device. Exhaust gas treatment equipment for paint drying ovens installed.